If the search results are different from your expectations (e.g. no subtasks found, although there are some) this is usually due to the problems with permission configuration.
In order to perform correctly, the app must have Browse Project and Edit Issues permissions for all projects searched.
There is one place to check to ensure that the app has the required permissions to run: Project Permission Scheme
Project Permission Scheme
Find the permission scheme associated with the projects on which the app isn't working correctly (there may be multiple permission schemes to fix for multiple projects).
Project → Project settings → Permissions
Ensure that the project role atlassian-addon-project-access is there. If not, grant Browse Projects and Edit Issue to this project role.